METALLURGY OP IRON AND STEEL. greater waste of iron. This oxidation is not always objectionable, for, if the charge contains an excess of pig-iron, some agent must be used to burn the silicon and carbon. A gas containing hydrogen, like natural gas or petroleum, will be more efficient in this work than a dry carbonic oxide flame, while an excess of steam will make the action still more rapid; but its use is not to be recommended, for a considerable proportion of the oxide of iron will unite with the silica of the hearth and be lost beyond recovery. It is better to have no free steam during the melting of the charge, while, after the melting is done, the oxygen may be supplied in the form of ore with more satisfactory results. The metal at the time of tapping should be as nearly as possible in the condition of steel in a crucible during the "dead melt," and this can only be attained by a neutral flame. In spite of the opinions of many metallurgists, such a flame cannot be obtained for any length of time, since it'has no active calorific power, and even when black smoke is pouring from the stack, the silicon, man- Longitudinal Section through Center of Furnace. XI, Et, air chambers; F, Fv gas chambers; H, gas port; I, air port; JT. furnace hearth; L, flues to valves; M, M, binding rods; 0T meeting place of gas and air. FIG. "VTII-A.óBAD TYPE OF AN OPEN-HEARTH FURNACE.